Method of making charge-coupled device with microlens

ABSTRACT

A CCD and manufacturing method thereof is disclosed including: a first conductivity-type substrate having a convex portion; a first conductivity-type charge transmission domain formed on the substrate excluding the convex portion; a light detecting domain formed on the convex portion of the substrate and having a convex top surface; a second conductivity-type high-concentration impurity area formed on the top surface of the light detecting domain; a gate insulating layer formed on the substrate excluding the light detecting domain; a transmission gate formed on the gate insulating layer; a planarization layer formed on the substrate including the transmission gate; and a microlens formed on the planarization layer above a photodiode.

This application is a divisional of application Ser. No. 08/513,568, nowU.S. Pat. No. 5,693,767 filed on Aug. 10, 1995, the entire contents ofwhich are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a charge-coupled device (CCD), and moreparticularly, to a CCD and method of manufacturing the same whichprevents smear and improves sensitivity.

FIGS. 1A and 1B are sectional views of a conventional CCD. Referring toFIG. 1A, in the conventional CCD first and second p⁻ type wells 11 and12 are formed on an n type substrate 10. An n⁺ type photodiode 14 and n⁺type vertical charge coupled device (VCCD) 15, which is the chargetransmission domain, are formed on first and second p⁻ type wells 11 and12. A p⁺⁺ type surface isolation layer 16 is formed on n⁺ typephotodiode 14. A third p⁻ type well 13 is formed to surround n⁺ typeVCCD 15. A p⁺ type channel stop 17 is formed to insulate pixelstherebetween.

A gate insulator 18 is formed on the overall surface of the substrate. Atransmission gate 19, interlevel insulator 20 and light-shielding layer21 are formed sequentially on gate insulator 18 above VCCD 15. Apassivation layer 22 is formed on the overall surface of the substrate.

A first planarization layer 23 is formed on passivation layer 22. Acolor filter layer 24 is formed on first planarization layer 23 abovephotodiode 14. A second planarization layer 25 is formed on firstplanarization layer 23 including color filter layer 24. A microlens 26is formed on second planarization layer 25 above color filter layer 24.

In the conventional CCD, light coming through a camera lens is convergedby microlens 26 and passes through color filter layer 24. Lightselectively passing through color filter layer 24 is incident uponphotodiode 14, and photoelectrically converted into charges. Thesecharges produced from the photodiode through photoelectric conversionare transmitted to VCCD 15 and then vertically to a horizontal chargecoupled device (HCCD) by a clock signal of VCCD 15. The chargestransmitted to the HCCD (not shown) are horizontally transmitted by aclock signal of the HCCD. The horizontally transmitted charges aredetected as a voltage due to the device ends' floating diffusion. Thevoltage is amplified to be transmitted to the peripheral circuits.

As shown in FIG. 1B, in the conventional CCD, light incident upon thecenter of the microlens comes into photodiode 14 to be photoelectricallyconverted into signal charges. However, light incident on the peripheryof the microlens enters VCCD 15 and is photoelectrically converted intosmear charges. These smear charges cause the smear phenomenon. In caseof long-wavelength light, the light incident on microlens 26 passesthrough the photodiode and enters first p⁻ type well 11, producingundesirable signal charges. In addition, the step height in thephotodiode and VCCD becomes high.

SUMMARY OF THE INVENTION

Therefore, it is an object of the present invention to provide a CCD andmanufacturing method thereof in which the photodiode is formed like themicrolens, to thereby enhance photosensitivity.

It is another object of the present invention to provide a CCD andmanufacturing method thereof in which light converged by the microlensis focused only on the photodiode, to thereby prevent the smear.

To accomplish the objects of the present invention, there is provided aCCD comprising: a first conductivity-type substrate having a convexportion; a first conductivity-type charge transmission domain formed onthe substrate excluding the convex portion; a light detecting domainformed on the convex portion of the substrate and having a convex topsurface; a second conductivity-type high-concentration impurity areaformed on the top surface of the light detecting domain; a gateinsulating layer formed on the substrate excluding the light detectingdomain; a transmission gate formed on the gate insulating layer; aplanarization layer formed on the substrate including the transmissiongate; and a microlens formed on the planarization layer above aphotodiode.

For the present invention, there is provided a method of manufacturing aCCD comprising the steps of: etching a first conductivity-type substrateto thereby form a convex portion; ion-implanting a firstconductivity-type impurity into the substrate excluding the convexportion to thereby form a first conductivity-type charge transmissiondomain; sequentially forming a gate insulating layer and transmissiongate on the substrate above the charge transmission domain;ion-implanting a first conductivity-type impurity into the convexportion of the substrate, using the transmission gate as a mask, tothereby form a convex light detecting area; ion-implanting a secondconductivity-type high-concentration impurity into the light detectingarea to thereby form a second conductivity-type high-concentrationimpurity area on the surface of the light detecting area; forming aplanarization layer over the substrate; and forming a microlens on theplanarization layer above a photodiode.

BRIEF DESCRIPTION OF THE ATTACHED DRAWINGS

FIGS. 1A and 1B are sectional views of a conventional charge-coupleddevice;

FIGS. 2A and 2B are sectional views of one embodiment of thecharge-coupled device of the present invention; and

FIGS. 3A-3J show the manufacturing sequence of the charge-coupled deviceof the present invention shown in FIGS. 2A and 2B.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, a preferred embodiment of the present invention will bedescribed with reference to the attached drawings.

Referring to FIG. 2A, first and second p⁻ type wells 31 and 32 areformed on an n type substrate 30. A convex photodiode 34 is formed onfirst p⁻ type well 31. A VCCD 35, a charge transmission domain, isformed on second p⁻ type well 32.

A p⁺⁺ type surface isolation layer 37 is formed on the convex surface ofphotodiode 34. A gate insulating layer 38, transmission gate 39 andlight-shielding layer 41 are formed on the substrate excluding theconvex surface of the photodiode. An interlevel insulating layer 40 isformed between transmission gate 39 and light-shielding layer 41.

A passivation layer 42 is formed on the overall surface of thesubstrate. A first planarization layer 43 is formed on passivation layer42. A color filter layer 44 is formed on first planarization layer 43above the photodiode. A second planarization layer 45 is formed on firstplanarization layer 43 including color filter layer 44. A microlens 46is formed on second planarization layer 45 above the color filter layer.

In the CCD of the present invention, photodiode 34 has a convex topsurface to be formed like microlens 46, increasing the light receivingarea as compared with the photodiode of the conventional CCD shown inFIGS. 1A and 1B.

In addition, the distance between the microlens and photodiode isshortened because the photodiode is convex. For this reason, as shown inFIG. 2B, the light converged by microlens 46 is focused only onphotodiode 34 and long-wavelength light is incident only upon thephotodiode, preventing the smear. Furthermore, the convex top surface ofthe photodiode improves the step height in the photodiode and VCCD,facilitating the succeeding process.

Now, referring to FIG. 3A, first and second p⁻ type wells 31 and 32 aresequentially formed on n type substrate 30. A material 51 for themicrolens is coated and patterned on the overall surface of thesubstrate. The material for the microlens is left only on the substrateabove first p⁻ type well 31. Here, first p⁻ type well 31 is formed byfirst ion implanting a p⁻ type impurity into substrate 30. Second p⁻type well 32 is formed by second ion implanting a p⁻ type impurity intosubstrate 30 excluding first p⁻ type well 31. Second p⁻ type well 32 hasa junction depth deeper than that of first p⁻ type well 31.

When microlens material 51 flows thermally at 100°-200° C., microlens 51is formed on the substrate above first p⁻ type well 31, as shown in FIG.3B. When the substrate in which microlens 52 is formed is dry-etched toetch all of microlens 52, the substrate has a convex portion 30-1, asshown in FIG. 3C. Here, the photodiode will be formed in convex portion30-1 according to the succeeding process.

Referring to FIG. 3D, p⁺ type channel stop 37 is formed to insulatepixels therebetween. Subsequently, as shown in FIG. 3E, p⁺ type impurityand n⁺ type impurity are ion-implanted into substrate 30 excludingconvex portion 30-1, to thereby form third p⁻ type well 33 and n⁺ typeVCCD 35.

As shown in FIG. 3F, gate insulator 38 of oxide layer and nitride layeris formed on the substrate excluding convex portion 30-1. Then, apolysilicon layer is deposited and patterned on the overall surface ofthe substrate, to thereby form transmission gate 39 on gate insulator38.

In FIG. 3G, using transmission gate 39 as a mask, n⁺ type impurity ision-implanted into convex portion 30-1 of the substrate to thereby formn⁺⁺ type photodiode 34. Using transmission gate 39 as a mask, p⁺⁺ typeimpurity is ion-implanted into photodiode 34 to thereby form p⁺⁺ typesurface isolation layer 36 on the surface of photodiode 34.

Subsequently, referring to FIG. 3H, interlevel insulating layer 40 isformed on transmission gate 39 excluding the convex top surface ofphotodiode 34. The overall surface of the substrate is coated of a metallayer and patterned to thereby form light-shielding layer 41 oninsulating layer 40.

As shown in FIG. 3H, a nitride layer is deposited on the overall surfaceof the substrate to form passivation layer 42. First planarization layer43 is formed thereon. Color filter layer 44 is formed on firstplanarization layer 43 above photodiode 34.

Second planarization layer 45 is formed on first planarization layer 43including color filter layer 44. Finally, through a general process offorming a microlens, microlens 46 is formed on second planarizationlayer 45 above color filter layer 44, finishing manufacturing the CCD ofthe present invention.

As described above, the present invention has the following effects.

First, the light receiving area of the photodiode is increased ascompared with the conventional CCD because the photodiode is formed likethe microlens. This improves photosensitivity.

Second, the step height of the photodiode and VCCD is improved tofacilitate succeeding processes.

Third, the photodiode is formed convex to shorten the distance betweenthe microlens and photodiode, as compared with the conventional CCD.Therefore, light converged by the microlens including thelong-wavelength light all is incident only upon the photodiode,completely suppressing the smear.

What is claimed is:
 1. A method of manufacturing a CCD comprising thesteps of:etching a first conductivity-type substrate to thereby form aconvex portion; ion-implanting a first conductivity-type impurity intosaid substrate excluding said convex portion to thereby form a firstconductivity-type charge transmission domain; sequentially forming agate insulating layer and transmission gate on said substrate above saidcharge transmission domain; ion-implanting a first conductivity-typeimpurity into said convex portion of said substrate, using saidtransmission gate as a mask, to thereby form a convex light detectingarea; ion-implanting a second conductivity-type high-concentrationimpurity into said light detecting area to thereby form a secondconductivity-type high-concentration impurity area on the surface ofsaid light detecting area; forming a planarization layer over saidsubstrate; and forming a microlens on said planarization layer above aphotodiode.
 2. A method of manufacturing a CCD as claimed in claim 1,wherein said step of forming said convex portion on said substratecomprises the substeps of:coating a microlens material on saidsubstrate; patterning said microlens material to be left only on aportion corresponding to said light detecting area; thermally flowingsaid microlens material to thereby form said microlens on saidsubstrate; dry-etching said substrate to thereby remove said microlensand simultaneously form a convex portion on a portion where saidmicrolens is removed.
 3. A method of manufacturing a CCD as claimed inclaim 1, after the step of forming said transmission gate, furthercomprising a step of forming a light-shielding layer on said substrateexcluding said light detecting area.
 4. A method of manufacturing a CCDas claimed in claim 1, after the step of forming said planarizationlayer, further comprising a step of forming a color filter layer on saidplanarization layer above said light detecting area.